What is Alzheimer's Disease?

Alzheimer’s Disease is the leading cause of dementia in adults, and accounts for 60-80% of all dementia cases (Alzheimer’s Association, 2025). The population primarily affected by this disease includes individuals 65 and older. It is characterized by cognitive decline and memory loss. These symptoms, if left untreated, worsen over time. In severe cases an individual may have difficulty swallowing or talking, and have many episodes of confusion or disorientation. 

This disorder is due to improper neuronal function caused by abnormal protein build up in the brain. Amyloid protein is responsible for the plaque built between neurons, while tau proteins form tangles within neurons (NHS, 2021). Plaque inhibits signaling between synapses, while tau proteins prevent cellular transport within a neuron. This leads to improper function and cell death.  

Although there is not an exact known cause, there are more than likely a number of factors that play a role in disease development, including genetics, environment, cardiovascular disease, etc. (National Institute on Aging, 2024)

Epigenetic mechanisms, genetic variants, and lifestyle choices contribute to this neurodegenerative disease (Santana et al., 2023). Following an epigenome-wide assessment of DNA methylation, researchers had strong evidence of hypermethylation within HOXB6 gene (Roubroeks et al., 2020).  

In early onset (familial Alzheimer’s) this autosomal dominant inheritance will result in an individual inheriting mutations in one of the following genes: -presenilin 1 (PSEN1) -presenilin 2 (PSEN2) -amyloid precursor protein (APP) (Kelleher & Shen, 2017). 

PSEN1 and PSEN2 affect enzymatic activity that directly interacts with APP. This causes amyloid-beta fragments to buildup in the brain. Furthermore, mutations in APP will directly lead to plaque buildup (Kelleher & Shen, 2017). 

Late onset Alzheimer’s has another genetic cause. A variant of APOE (apolipoprotein E.) gene known as APOE e4, is associated with late onset Alzheimer’s. Its main function is transporting cholesterol into the blood (De Jager et al., 2014). 

Epigenetic factors such as CpG regions have been looked at in ABCA7 and BIN1. One particular study indicated several genes whose RNA expression changed ANK1, RHBDF2, RPL13 (De Jager et al., 2014).